1. Field of the Invention
The present invention relates, in general terms, to the handling of fluid materials under pressure. In a more particular sense, the invention is a valve designed especially for use in the blast-finishing field. In this industry, a wide variety of surfaces must be blasted with abrasive media for removing scale, rust, old paint, or the like, to prepare the surface for re-coating or other protective or conditioning procedures. The valve of the present invention is one in which manual and automatic control assemblies can be readily interchanged. In the automatic configuration, the valve incorporates a diaphragm which cooperates with a spring and with the pressure maintained in a blast hose, to regulate the insertion of media into the pressurized flow through the hose with a high degree of precision.
2. Description of the Prior Art
In the field in which the valve of the present invention is designed to function with particular effectiveness, many valves have been provided for the purpose of metering the flow of abrasive media into a blast hose. However, the valves previously devised, though in many cases functioning satisfactorily, have evidenced certain disadvantages.
A valve used to control the flow of abrasive media should desirably be designed in a manner to minimize wear on the parts of the valve resulting from contact with the media, and should facilitate the replacement of those parts. Heretofore, the valves commonly used in the blast-finishing field have had the disadvantages of presenting surfaces against which the media are directed, sometimes frontally and in other instances obliquely. In either event, this subjects the surfaces, against which the media are propelled at high velocity and under heavy pressures, to excessive wear. As a result, prior art valves of this type soon malfunction or lose their full efficiency. They consequently require total replacement, or in other instances require replacement of expensive components to which access is had with considerable difficulty.
The valves of the prior art, further, are of relatively complex construction, and yet have proved deficient as regards precise metering or regulation of the abrasive media into the pressurized carrier air directed through the blast hose. Especially are these deficiencies noted when the blasting operation is being carried out under difficult conditions and in particular with coarse media.